Dynamics of keyhole and molten pool in laser welding

In laser and electron-beam welding, a deep cavity called a keyhole or beam hole is formed in the weld pool due to the intense recoil pressure of evapo ration. The formation of the keyhole leads to a deep penetration weld with a high aspect ratio and this is the most advantageous feature of welding by high-energy-density beams. However, a hole drilled in a liquid is primaril y unstable by its nature and the instability of the keyhole also causes the formation of porosity or cavities in the weld metal. In particular, the po rosity formation is one of the serious problems in very high-power laser we lding, but its mechanism has not been well understood. The authors have con ducted systematic studies on observation of keyhole as well as weld pool dy namics and their related phenomena to reveal the mechanism of porosity form ation and its suppression methods. The article will describe the real-time observation of keyhole and plume behaviors in the pulsed and continuous-wav e laser welding by high-speed optical and x-ray transmission methods, the c avity formation process and its suppression measures. (C) 1998 Laser Instit ute of America. [S1042-346X(98)00706-2].